We have already discovered a light- and ADP-dependent inhibition of the ATPase and phosphorylation activities of the coupling factor of isolated spinach chloroplasts, by permanganate ions at a low concentration, possibly affecting a group(s) at the inorganic phosphate binding site. Attempts will be made to find out which amino acids are affected, and on which subunits of this complex enzyme. Attempts will be made to bind fluorescent or spin-label probe molecules covalently to the coupling factor, and see if these are able to report the kinetics of the conformational change previously detected by hydrogen (tritium) exchange studies. A further exploration of parameters governing the re-binding of coupling factor protein to depleted membranes is planned. Work may be initiated on specific labelling of amino groups of the coupling factor.